Journal of Superconductivity and Novel Magnetism最新文献

Cesium based double perovskites are important for their tunable optoelectronic attributes, magnetic ability, stability, and lead-free composition, making them promising materials for sustainable photovoltaic and spintronic applications. We have examined in detail the physical characteristics of the cubic Cs₂LiMoBr₆ double perovskite. The structural stable phase is verified through the structural stability parameters. Furthermore, information about the interaction of material with electromagnetic radiation is revealed by the optical properties. The optical characteristics predict their peak response in the UV range. A direct bandgap has been measured with a spin-up of 2.25 eV and a spin-down of 3.56 eV. Based on the magnetic moments of 3.00173 µB, Cs₂LiMoBr₆ is a promising material for use in spintronic devices. The transport traits are also assessed, presenting large ZT values at high temperatures for spin-up and large ZT at low temperatures for spin-dn. Based on the aforementioned characteristics, Cs₂LiMoBr₆ is a reasonable choice for optoelectronic, thermoelectric and spintronic applications.

This study presents a comprehensive first-principles investigation of the electronic, magnetic, and structural properties of manganese-doped zinc oxide (Mn_xZn_1-xO) using Density Functional Theory (DFT) with the Local Spin Density Approximation and Hubbard U correction (LSDA + U). By modeling supercells ranging from 32 to 192 atoms, we systematically analyzed the effects of Mn concentration (from 1.04% to 12.5%). The electronic structure calculations reveal that Mn doping induces significant spin polarization. At low concentrations (≤ 6.25%), the system behaves as a spin-split semiconductor, with the calculated spin-down band gap for ~ 2% Mn doping (3.54 eV) showing excellent agreement with experimental photoluminescence data (3.53 eV). In contrast, at a high concentration of 12.5%, the system transitions to a metallic state. Magnetic property analysis shows that each Mn dopant introduces a localized magnetic moment of approximately 4.8–4.9 µ_B, consistent with a high-spin Mn²⁺ state, and induces minor spin polarization on neighboring oxygen atoms, indicating p-d hybridization. Our calculations reveal a delicate competition between ferromagnetic (FM) and antiferromagnetic (AFM) ordering, with the magnetic ground state alternating as a function of Mn concentration. Stability analysis, based on formation and cohesive energies, confirms that Mn substitution in the ZnO lattice is thermodynamically favorable and structurally stable across all concentrations studied. However, the Curie temperatures estimated for the FM-stable configurations are very low (< 4 K). These findings suggest that while Mn-doped ZnO is structurally stable and possesses tunable spin-polarized electronic properties, it is intrinsically paramagnetic at room temperature in its pristine, defect-free form. Achieving robust ferromagnetism likely requires extrinsic factors such as defect engineering.

Chalcogenide perovskites have recently emerged as a promising family of functional materials owing to their tunable electronic structures, chemical stability, and potential in thermoelectric, optoelectronic, and protective-coating applications. In this work, we present a comprehensive first-principles investigation of the structural, mechanical, thermal, electronic and optical properties of the chalcogenide perovskites BaTaS₃ and BaNbS₃ using density functional theory (DFT). The optimized lattice parameters for BaTaS₃ (a = 6.948 Å, c = 5.709 Å) and BaNbS₃ (a = 6.932 Å, c = 5.749 Å) agree well with available literature. Both compounds crystallize in the orthorhombic phase and exhibit metallic electronic characteristics. The calculated elastic constants satisfy the Born stability criteria, confirming their mechanical stability, while moderate elastic anisotropy is observed from the directional dependence of Young’s modulus. The evaluated bulk, shear, and Young’s moduli reveal that BaNbS₃ is mechanically stiffer than BaTaS₃. The Debye temperatures were estimated to be 309.2 K (BaTaS₃) and 330.8 K (BaNbS₃), while the minimum lattice thermal conductivities were calculated as 2.7 and 2.88 W m⁻¹ K⁻¹, respectively. Optical analysis reveals high reflectivity (> 65%) in the visible–UV region and pronounced plasma resonance peaks at ~ 15 eV. These quantitative results position BaTaS₃ and BaNbS₃ as promising chalcogenide perovskites for thermal-management and reflective-coating applications. Optical properties including the dielectric function, absorption coefficient, reflectivity, and energy-loss spectra were analyzed up to 50 eV, revealing strong metallic reflectivity and a pronounced plasma resonance in the ultraviolet region. These results provide a detailed understanding of the intrinsic physical properties of BaTaS₃ and BaNbS₃ and establish them as representative members of the chalcogenide perovskite class for future theoretical and experimental exploration.

The physical, morphological, optical, and magnetic characteristics of zinc oxide (ZnO) nanoparticles co-doped with yttrium (Y) and neodymium (Nd) are examined in this work. The nanoparticles are synthesized using the co-precipitation technique with and without the addition of ethylenediaminetetraacetic acid (EDTA). For structure identification, X-ray diffraction (XRD) was used. The hexagonal wurtzite structure of ZnO was verified with successful Y and Nd inclusion, as well as a discernible decrease in crystallite size from 25.71 nm (x = 0) to 20.78 nm (x = 0.04) in uncapped samples, and from 32.72 nm (x = 0) to 18.46 nm (x = 0.04) in samples added with EDTA. Because of EDTA’s capping properties, morphological analyses using transmission electron microscope (TEM) showed that the EDTA-ZnO samples contained smaller, more homogeneous particles. Band gap narrowing and an absorption edge redshift were detected by UV-Vis spectroscopy, indicating changed optical behaviour, with extracted band gaps varying between 2.46 and 2.88 eV for uncapped and 2.71–2.89 eV for EDTA-capped systems. An agglomerated non-homogeneous morphology combining spherical and needle-like forms was observed in co-doped samples. Fourier transform infrared spectroscopy (FTIR) was used to confirm the vibrational characteristics. Because of the O-H group present in the EDTA molecules, EDTA-capped ZnO samples also had an extra OH vibration band and an additional ester carbonyl band at 1745 cm^− 1 due to EDTA coordination. Co-doped and EDTA-modified materials showed a reduced band gap and a redshift in absorption, according to UV-Vis spectroscopy. Vibrating sample magnetometer (VSM) magnetic studies revealed weak room-temperature ferromagnetism with saturation magnetization varying from 32.4 × 10^− 3 emu/g (x = 0) to 18.419 × 10^− 3 emu/g for x = 0.04 for uncapped samples, while EDTA-capped samples reached 39.43 × 10^− 3 emu/g at x = 0.04, indicating enhanced magnetic response due to oxygen-vacancy concentration and dopant interaction.

The recently emerged field of Terahertz spectroscopy provides an important tool for studying the relaxation and various excitations at a previously inaccessible energy scale which is especially important in superconductors. Sufficiently strong fields allow to examine nonlinear effects such as higher harmonic generation. In this work, we study the photoinduced current resulting from an exposure of a clean and uniform conducting material to sufficiently strong radiation. The phenomenon of photoinduced current can be observed in either bulk non-centrosymmetric materials or in certain sample geometries where a designated direction is introduced, for example, thin films. We explore the implications of the approximate electron momentum conservation in clean metals. We find a universal relation which expresses the essentially nonlinear zero frequency photoinduced current through the first-order conductivity in non-isotropic geometries where it is facilitated by the excitation of plasma modes. Our results are relevant for various clean materials and can be directly checked in experiments on photocurrent measurements.

For an epitaxial film of an electron-doped superconductor ({text{Nd}}_{2-x}{text{Ce}}_{x }{text{CuO}}_{4}) (x = 0.145), in a mixed state, a well-defined step structure is observed on the dependence of the c-axis resistance on the magnetic field parallel to CuO₂ layers. It is shown that in the region of the free flow of Josephson vortices, an exponential dependence of monotonous ({R}_{c}(B)) component in the flux-flow mode is observed. The "quantized" steps of equal height in the actual range of magnetic fields were registered with a period of (Delta Bsim {Phi }_{0}/left({lambda }_{ab}{lambda }_{c}right)) where the magnetic penetration depths in the ab-plane (({lambda }_{ab})) and along the c-axis (({lambda }_{c})) determine the sizes of the Josephson vortices in anisotropic layered superconductor. We associate the periodic steps of magnetoresistance with the resonant response of the system under study to the magnetic field-induced change in the number of Josephson vortices, each of which contains a magnetic flux quantum.

The evolution with interaction of the electronic structure of the triangular Hubbard model, which is believed to be the parent model for describing the electronic structure of twisted bilayer dichalcogenides, is studied within the cluster perturbation theory using 13-site clusters. Local and non-local correlations are taken into account within a cluster, while the intercluster hopping is considered using perturbation theory. We obtain the evolution of the electronic structure from metal to insulator through the pseudogap state with increasing interaction. We show that this pseudogap state is characterized by the arc–like Fermi surface with maximum spectral weight located in the (Gamma -K) directions. The energy distribution curves at the Fermi level are not characterized by a strong spectral function peak. Such momentum-dependent behavior of pseudogap suppression of spectral function is not typical for the most familiar pseudogap in doped cuprates in the presence of strong antiferromagnetic correlations and can lead to momentum-uniform pseudogap.

To analyze the effect of sodium doping on iron-selenide 122 superconductors family we have grown crystals of (Na, K, Rb)Fe₂Se₂. Using resistive and magnetic probes it was confirmed that Na_0.27K_0.27Rb_0.27Fe₂Se₂ shows high quality and homogeneity of the superconducting properties below T_c ≈ 32 K. The morphology and composition were studied for this sample as seen via electron microscopy and showed the presence of a new sodium-rich phase.

Ce_1 − xFe_xO₂ (x ≤ 0.05) nanoparticles were synthesized via chemical co-precipitation and characterized for structural, thermal, optical, and magnetic properties. XRD confirmed a single-phase cubic fluorite structure, while EDX verified near-stoichiometric composition. FE-SEM and TEM showed uniformly distributed nanocrystals (~ 11 nm). TGA with Coats-Redfern analysis indicated enhanced oxygen-ion mobility and defect-assisted thermal behavior for Ce_0.95Fe_0.05O₂ (Eₐ = 7.91 kJ) compared to CeO₂ (Eₐ = 10.38 kJ). Optical studies revealed a band gap reduction (2.82 → 2.58 eV) and improved visible-light absorption with Fe doping. The magnetic parameters (M_s ~ 0.003–0.004 emu/g, H_c ~ 250–300 Oe) confirm the presence of weak, defect-mediated ferromagnetism originating from oxygen-vacancy-induced F-center exchange. Compared with earlier sol-gel and hydrothermal Fe–CeO₂ reports, this work uniquely correlates co-precipitation–derived oxygen vacancy density with thermodynamic and magnetic behavior. These results highlight the role of defect engineering in tuning the multifunctional properties of Fe-doped CeO₂ for spintronic applications.